1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display (LCD) device, and more particularly, to a reference voltage generating circuit for an LCD device. Embodiments of the present invention are suitable for a wide scope of applications. In particular, embodiments of the present invention are suitable for generating and maintaining voltages at a plurality of levels for the LCD device.
2. Discussion of Related Art
In general, a signal processing and control system uses a reference voltage signal to detect a desired signal. The signal processing and control system periodically changes signal modes and control states as needed. Accordingly, the reference voltage signal may alternate between at least two voltage levels depending on the number of states and signal modes.
A liquid crystal display device, which may include a signal processing and control system, uses “a common voltage” as a reference voltage alternating between two different voltage levels. In particular, the common voltage swings between the two levels corresponding to pixel data voltages of positive polarity and negative polarity supplied to liquid crystal cells. Thus, the swing type common voltage allows the pixel date voltages of the positive polarity and the negative polarity to share a predetermined voltage level region. The liquid crystal display device not only displays an image of an excellent quality but also remarkably reduces the power consumption by using the swing type common voltage. In order to generate the swing type common voltage, the liquid crystal display device uses a common voltage generating circuit including a high capacity transistor, such as a transistor having a wide channel.
The high capacity transistor provided in the related art common voltage generating circuit can shorten the level transition period of the common voltage but cannot maintain a stable transition level. Specifically, the common voltage oscillates and vibrates in the vicinity of the transition level in the related art common voltage generating circuit. The oscillation phenomenon adds a noise component to a pixel data voltage and deteriorates the quality of the displayed image on the LCD device.